Silver halide emulsions containing alkyl esters of benzimidazole carbamic acid antifogging agents



United States Patent 3,499,761 SILVER HALIDE EMULSIONS CONTAINING AL- KYL ESTERS 0F BENZIMIDAZOLE CARBAMIC ACID ANTIFOGGING AGENTS Fritz Dersch, Binghamton, and Sally L. Paniccia, Endwell, N.Y., assignors to GAF Corporation, New York, N.Y., a corporation of Delaware No Drawing. Filed July 20, 1964, Ser. No. 383,963 Int. Cl. G03c 1/34, 5/30 US. Cl. 96--66.5 17 Claims ABSTRACT OF THE DISCLOSURE A light sensitive photographic material comprising a silver halide emulsion and an anti-foggant compound contained therein, or in a layer contiguous therewith; the anti-foggant being an alkyl ester of benzimidazole carbamic acid.

The present invention relates, in general, to photographic materials comprising light-sensitive silver halide emulsions and, in particular, to stabilized silver halide emulsions which have less tendency to fog without substantial reduction in the light sensitivity thereof.

It is well established that light sensitive emulsions such as gelatin-silver halide emulsions are subject to fogging. Fogging in general and chemical fogging in particular may be defined as a uniform deposit of silver extending over and either partially or wholly obliterating the image and is caused in a number of ways; namely the nature of the emulsion, its age and the conditions under which it has been stored, the nature of the developer, impurities in the developing solution, and the time and temperature of the development. Additionally, chemical fogging is also promoted when such active agents as metol are employed in a concentrated solution or are used in the presence of an excess of alkali. Similarly, the oxidation of certain developing agents such as metol and hydroquinone exerts a powerful fogging action.

While a great number of antifoggants and stabilizers have been heretofore suggested as effective in preventing an increase in fogging and as a result thereof stabilize or control the keeping qualities of light sensitive silver halide emulsions, many of these compounds lower the sensitivity of silver halide emulsions and reduce the optical or dye sensitizing ability of the emulsions.

Accordingly, it is a primary object of this invention to provide stabilizers or fog inhibiting agents which tend to prevent the formation of chemical fog in light-sensitive silver halide emulsions.

A further object is to provide stabilizers or antifogging agents for light-sensitive silver halide emulsions which do not appreciably lower the sensitivity of the silver halide emulsions.

Yet another object is to provide a stabilizer or antifoggant which, when added to photographic gelatin or to photographic emulsion, will prevent speed loss of the emulsion during its storage.

A still further object is to provide stabilizers or antifogging agents for light-sensitive silver halide emulsions which do not reduce the sensitivity to light of longer wave length affected by the presence of sensitizing dyes.

Still further objects and advantages will become further apparent from the following detailed description thereof.

It has been discovered that the above objects are readily accomplished by intimately associating with silver halide emulsions certain alkyl esters of benzimidazole carbamic acids of the following formula:

Y NH

wherein X is hydrogen, a halo radical such as chloro, fiuoro, bromo or iodo radicals and alkyl or alkoxy radicals containing less than seven carbon atoms in the alkyl group, n is a whole positive integer of less than four, R represents hydrogen, potassium, sodium, ammonium or lower aliphatic hydrocarbon radicals such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, or amyl; and Y represents hydrogen, chloro, nitro, methyl or ethyl radicals.

While the above general formula is indicative of the class of benzimidazole carbamic acids operable to produce the antifogging effects observed, it is generally believed that such effects are attributable to the presence in the silver halide emulsions of the benzimidazole structure and not necessarily dependent upon the length or particular configuration of the substituents X, Y and R although their presence in the nucleus cannot entirely be discounted.

Typical and representative compounds within the scope of the general formula set forth above include:

' benzimidazole-Z-car-bamic acid, isoamyl ester benzimidazole-Z-carbarnic acid, hexyl ester 5-methyl-6-nitrobenzimidazole-Z-carbamie acid, hexyl ester 4,6-dichlorobenzimidazole-2-carbamic acid, propyl ester 5-fiuorobenzimidazole-Z-carbamic acid, methyl ester 4-nitrobenzimidazole-2-carbamic acid, ethyl ester 4,7-dichloro-S-methylbenzimidazole-Z-carbamic acid amyl ester 1 5,7-dimethyl-4-chlorobenzimidazole-Z-carbamic acid,

isopropyl ester S-methoxybenzimidazole-2-carbamic acid, methyl ester 4,5,6,7-tetrachlorobenzimidazole-2-carbamic acid, butyl ester 5,6-dichloro-4-isopropoxybenzimidazole-Z-carbamic acid;

methyl ester S-bromo-6-butylbenzimidazole-Z-carbamic acid, ethyl ester 4,5,6,7-tetramethylbenzimidazole-Z-carbamic acid,

isobutyl ester Beneficial effects in fog reduction are obtained when solutions of the antifoggant are incorporated into the silver halide emulsions as ripening finals or as coating finals. Ripening finals are added during the ripening or the sensitivity increasing stage of the emulsion making process, whereas .coating finals are added to the silver halide emulsion just prior to the coating of the emulsion on a suitable support, such as, for example, paper, glass or film.

The addition of the antifoggants can be made before,

during or after the addition of the soluble silver salt to the soluble halide in the presence of a suitable carrier or colloid such as gelatin, polyvinyl alcohol, solubilized casein, albumin, and the like.

If desired, the antifoggants of the present invention can also be employed as components of the developing solution.

The amount of antifogging agent employed as additives to the light sensitive emulsions varies from about 0.1 to about 50 milligrams of antifoggant per 0.6 mole of silver halide. When the antifogging agents are employed as ripening finals it has been found advantageous to employ them in amounts in the range of from about 0.1 to about 25 milligrams per 0.6 mole of silver halide, whereas when the antifogging agents are employed in coating finals, it has been found advantageous to employ amounts in the range of from about 0.5 to about 50 milligrams of antifoggant per 0.6 mole of silver halide. Obviously, the development of optimum characteristics within the ranges set forth above will depend, in part, upon the type of emulsion employed and can be readily determined in each case.

In some cases, it has been found advantageous to apply the antifogging agents of the invention to adjacent layers, for example, in a separate undercoating layer or in the antiabrasion gelatin surface. Alternatively, it has been found advantageous, in some cases, to apply the antifogging agents of the invention in one or all processing baths or in pre and post baths.

It has also been found that the antifogging agents of the invention can be compatibly employed in combination with other known antifoggants and stabilizers; with sulfur, reductionand metal-, and noble metal sensitizers as well as in combination with polyoxyalkylene polyols, their derivatives; polyvinylpyrrolidones and other accelerators.

The following examples will serve to illustrate the practice of the invention:

EXAMPLE I A silver halide emulsion in gelatin containing 2% silver iodide and 98% silver bromide Was prepared in a conventional manner and brought up to its maximum light sensitivity. It was then readied for coating, finals were added, such as sensitizing dyes and hardening agents. A 0.1% solution of benzimidazole-2-carbamic acid, ethyl ester was added to the emulsion as an antifoggant and stabilizer.

The so-prepared emulsion samples were coated on a suitable cellulose ester base and dried. Samples of these film coatings were then exposed in a Type IB Sensitometer and developed in a developer of the following composition:

A silver halide emulsion in gelatin containing 2% silver iodide and 98% silver bromide was coated on film base in a manner known to the art. After the coating, a solution containing 20 grams of gelatin in 1 liter of H and a 0.1% solution of benzimidaz le-z-ca bamic acid.

ethyl ester was coated thereon as an anti-abrasion layer. After drying, film samples were exposed and processed as described in Example I. The samples exhibited no speed loss in oven storage tests with a fog reduction of 0.02 compared to a speed loss from to 88 with the stabilizers presently in use.

EXAMPLE III An emulsion was prepared and coated in the manner described in Example I, but development was carried out at a temperature of F. In this case, the type, which did not include an antifoggant, developed to a fog of 0.48, Whereas when 1 mg. of ethyl ester was used per kilo of emulsion the sample developed to a fog of only 0.28, with less speed loss than the type.

The antifogging agents which have been found to provide beneficial effects when incorporated into light sensitive silver halide emulsions can be readily prepared by known procedures such as described in US. 3,010,968, issued Nov. 28, 1961.

Various modifications of the invention will occur to persons skilled in the art. Thus, it is evident in lieu of the compounds of the specific examples, any of the compounds mentioned above can be employed with similar results. Therefore, it is not intended that the invention be limited in the patent granted except as necessitated by the appended claims.

What is claimed is:

1. A light sensitive photographic material comprising a light sensitive silver halide emulsion, a carrier therefor and an antifoggant characterized by the general formula:

Y NH

wherein X represents a member of the group consisting of hydrogen, chloro, fluoro, bromo, iodo and alkyl and alkoxy radicals containing less than seven carbon atoms, n is a whole positive integer of less than four, R represents a member selected from the group consisting of hydrogen, potassium, sodium, ammonium and aliphatic hydrocarbon radicals containing from one to six carbon atoms, and Y represents a member selected from the group consisting of hydrogen, chloro, nitro, methyl, ethyl and propyl.

2. The material as defined in claim 1 wherein the antifoggant is located in the silver halide emulsion.

3. The material as defined in claim 1 wherein the antifoggant is located in a layer adjacent the silver halide emulsion.

4. A light sensitive photographic material comprising a light sensitive silver halide emulsion and a carrier therefor, said emulsion containing, as an antifoggant, benzimidazole-Z-carbamic acid, ethyl ester.

5. A light sensitive photographic material comprising a light sensitive ilver halide emulsion and a carrier therefor, said emulsion containing, as an antifoggant, S-methyl- 6-nitrobenzimadazole-Z-carbamic acid, hexyl ester.

6. A light sensitive photographic material comprising a light sensitive silver halide emulsion and a carrier therefor, said emulsion containing, as an antifoggant, 4,6-dichlorobenzimidazole-Z-carbamic acid, propyl ester.

7. A light sensitive photographic material comprising a light sensitive silver halide emulsion and a carrier therefor, said emulsion containing, as an antifoggant, S-fluorobenzimidazole-2-carbamic acid, methyl ester.

8. A light sensitive photographic material comprising a light sensitive silver halide emulsion and a carrier there for, said emulsion containing, a an antifoggant, 4-nitrobenzimidazole-Z-carbamic acid, ethyl ester.

9. A light sensitive photographic material comprising a light sensitive silver halide emulsion and a carrier therefor, said emulsion containing, as an antifoggant, 4,7- dichloro-5-methylbenzimidazole 2 carbamic acid, amyl ester.

10. A light sensitive photographic material comprising a light sensitive silver halide emulsion and a carrier therefor, said emulsion containing as an antifoggant, 5,7-dimethyl-4-chlorobenzimidazole-Z-carbamic acid, isopropyl ester.

11. A light sensitive photographic material comprising a light sensitive silver halide emulsion and a carrier therefor, said emulsion containing, as an antifoggant, S-methoxybenzimidazole-Z-carbamic acid, methyl ester.

12. A light sensitive photographic material comprising a light sensitive silver halide emulsion and a carrier therefor, said emulsion containing, as an antifoggant, 4,5,6,7- tetrachlorobenzimidazole-Z-carbamic acid, butyl ester.

13. A light sensitive photographic material comprising a light sensitive silver halide emulsion and a carrier therefor, said emulsion containing, as an antifoggant, 5,6-dichloro 4 isopropoxybenzimidazole 2 carbamic acid, methyl ester.

14. A light sensitive photographic material comprising a light sensitive silver halide emulsion and a carrier therefor, said emulsion containing, as an antifoggant, 5-bromo- 6-butylbenzimidazole-Z-carbamic acid, ethyl ester.

15. A light sensitive photographic material comprising a light sensitive silver halide emulsion and a carrier therefor, said emulsion containing, as an antifoggant, 4,5, 6,7- tetramethylbenzimidazole-Z-carbamic acid, isobutyl ester.

16. A process of minimizing and preventing fog in light sensitive silver halide materials comprising a base having a light sensitive silver halide emulsion thereon, which comprises exposing said emulsion to light and developing the same in the presence of an antifoggant characterized by the formula:

wherein X represents a member of the group consisting of hydrogen, chloro, fluoro, bromo, iodo, :alkyl and alkoxy radicals containing less than seven carbon atoms in the alkyl group, n is a Whole positive integer of less than four, R represents a member selected from the group consisting of hydrogen, potassium, sodium, ammonium and aliphatic hydrocarbon radicals and Y represents a member selected from the group consisting of hydrogen, chloro, nitro, methyl, ethyl and propyl.

References Cited UNITED STATES PATENTS 3,023,103 2/1962 'Dersch et a1 96-109 3,137,578 6/1964 de Selms 96-109 3,255,202 6/1966 Johnson 96-109 3,271,154 9/1966 Dersch et al. 96-109 NORMAN G. TORCHIN, Primary Examiner R. E. FIGHTER, Assistant Examiner US. Cl. X.R. 96-109 

